1. Field of the Invention
The present invention relates to an apparatus for quantitatively determining body fat of a physical mass including a human body, an animal body or a fish body, and a method of quantitatively determining body fat of a physical mass other than a human body, and more particularly, it relates to an apparatus for and a method of non-invasively quantitatively measuring body fat with infrared light
2. Description of the Prior Art
In relation to methods of non-invasively measuring body fat, apparatuses for irradiating organisms with light of visible to near-infrared regions of 600 to 1100 nm and quantitatively determining body fat on the basis of absorbance by the body fat are proposed (refer to National Patent Publication Gazette No. 4-500762 (1992) and Japanese Patent Laying-Open Gazette No. 10-94523 (1998)).
In one of such methods, visible light having a central wavelength in the range of 660 to 740 nm is employed. The reason for this is that a light source is formed by a light emitting diode or the like having a large half-band width. The wavelength region is superior for maintaining or improving measurement accuracy since absorbance-change-per-unit-wavelength is flat. Consequently, since a low-priced light emitting diode can be obtained, it is assumed that the light emitting diode can be implemented at a low cost while maintaining high accuracy
Considering a physical mass including a human body, an animal body or a fish body, however, tissue components such as hemoglobin and melamine forming the physical mass have large absorption coefficients while the absorption coefficient of fat is small in this wavelength region.
Furthermore, the compositions of the tissue components subtly vary with measured regions or measuring persons, and hence the difference between the tissue components such as hemoglobin and melamine having large absorption coefficients exerts remarkable influence on the result of determination of the fat rate. In fact, it has been proven through measurements made by the inventors that no excellent correlation is obtained between a pannicular thickness and absorbance, and determination is difficult, not in the wavelength region, but even in a wavelength region exhibiting a larger absorption coefficient of fat (refer to FIG. 7 and description thereof made below).
The present invention is directed to a body fat measuring apparatus for measuring body fat of a physical mass including a human body, an animal body or a fish body, and a body fat measuring method of measuring body fat of a physical mass other than a human body, and an objective thereof is to improve quantitative determination accuracy for body fat.
The inventors have made measurements in a wavelength region exhibiting a large absorption coefficient by fat while varying a pressure for compressing a measured region or a peripheral portion thereof in two stages for obtaining the difference (difference absorbance) between absorbance values under the two compressed states, to find that there is correlation between the body fat and the difference absorbance.
FIG. 1 schematically expresses the present invention. A photometer 2 includes a projecting mechanism irradiating a physical mass with infrared light included in a wavelength region of 1.1 to 2.0 xcexcm, a photoreceiving mechanism receiving output light from the physical mass through the light and spectroscopic means separating the light applied to the physical mass or the output light from the physical mass into its spectral components, for measuring absorbance by the physical mass at a specific wavelength. A compression mechanism 4 can compress a measured region of the physical mass or a peripheral portion thereof, and difference absorbance calculator 6 obtains difference absorbance from first absorbance obtained by the photometer 2 under a state compressed by the compression mechanism 4 with a first pressure and second absorbance obtained by the photometer 2 under a state compressed with a second pressure lower than the first pressure or a non-compressed state. A storage part 8 stores relation between body fat and difference absorbance, and an operation part 10 determines quantitatively and outputs body fat from the difference absorbance calculated by the difference absorbance calculator 6 on the basis of the relation stored in the storage part 8.
The relation between body fat and difference absorbance is, for example, a relational equation showing correlation obtained from body fat measured by known means and the difference absorbance measured by the inventive apparatus and the storage part 8 stores such a relational equation for quantitative determination.
The term body fat includes a fat thickness and a fat rate.
A body fat measuring method according to the present invention is a method of quantitatively measuring body fat of a physical mass by carrying out a photometric step of irradiating a physical mass other than a human body with infrared light included in a wavelength region of 1.1 to 2.0 xcexcand receiving output light from the physical mass through the light for measuring absorbance by the physical mass at a specific wavelength under two states, i.e., a state compressed with a first pressure and a state compressed with a second pressure lower than the first pressure or a non-compressed state, obtaining difference absorbance from the difference between the absorbance values obtained under the respective states and quantitatively determining body fat on the basis of the difference absorbance.
In the wavelength region of 1.1 to 2.0 xcexcm, absorption coefficients of hemoglobin and melamine reduce and the absorption coefficient of fat increases. Therefore, measurement in this wavelength region is advantageous for quantitative determination of fat. While light absorption by tissue components other than fat is still present in the wavelength region of 1.1 to 2.0 xcexcm, fat can be quantitatively determined on the basis of difference absorbance by making measurement while varying the pressure for compressing the measured region or the peripheral portion thereof in two ages and obtaining the difference absorbance.
Thus, determination accuracy for fat is improved due to selection of the wavelength region exhibiting a large absorption coefficient of fat and difference absorbance obtained under two stages of compressed states.
The term xe2x80x9ccompressed statexe2x80x9d on a lower pressure side means not only compression under a low pressure but also a non-compressed state.
A body fat measuring apparatus according to the present invention is firstly directed to a human body. A pannicular thickness or a fat rate can be measured and utilized for health care or the like.
The body fat measuring apparatus according to the present invention is secondly directed to a physical mass other than a human body, i.e., the body of animals such as cows, pigs and whales, and/or fish such as tuna and yellowtail. The pannicular thickness or the fatty rate of such a live physical mass can be percutaneously measured for evaluating the quality as edible meat The apparatus is also applicable to percutaneous measurement in a carcass or dissociated state.
The body fat measuring method according to the present invention is directed to a physical mass other than a human body. This measuring method can be executed not only with the aforementioned measuring apparatus according to the present invention but also with another measuring apparatus.
FIG. 2 shows an absorption spectrum of beef tallow. In this spectrum, peaks xe2x80x9caxe2x80x9d and xe2x80x9ccxe2x80x9d are by fat and a peak xe2x80x9cbxe2x80x9d is by water. The peak top wavelength of the peak xe2x80x9caxe2x80x9d is around 1.21 xcexcm (8264 cmxe2x88x921), and the peak top wavelength of the peak xe2x80x9ccxe2x80x9d is around 1.72 xcexcm (5814 cmxe2x88x921). Therefore, a wavelength around 1.21 xcexcm or 1.72 xcexcm is preferably selected for measuring absorbance of fat.
When performing two-wavelength measurement, two wavelengths of a first wavelength (measuring wavelength) around 1.21 xcexcm or 1.72 xcexcm and a second wavelength (reference wavelength) exhibiting a small absorption coefficient of body fat are selected as wavelengths for measuring absorbance, and difference absorbance is obtained. Absorbance under each compressed state is preferably obtained by subtracting absorbance at the reference wavelength from absorbance at the measuring wavelength.
The reason for employing the difference between the absorbance at the measuring wavelength and the absorbance at the reference wavelength is as follows: In general, fluctuation of a baseline takes place in a spectrum. A temperature drift of an apparatus, ambient temperature change, deterioration of a light source, sensitivity change or deterioration of a detector caused by a temperature, change of a scattered state of a measured object, the degree of contact between the measured object and a measuring probe, reproducibility of the position of a measured region and the like can be listed as the causes. Therefore, when employing the difference between the absorbance at the measuring wavelength and the absorbance at the reference wavelength, these fluctuation factors are eliminated and absorbance can be measured with excellent reproducibility.
However, the present invention is not restricted to cases of employing the absorbance difference but also applicable to cases of obtaining difference absorbance under different compressed states on the basis of absorbance at the measuring wavelength.
The first pressure applied by the compression mechanism 4 is preferably set to 1.0 to 3.0 kPa, and the second pressure is preferably set to less than 1.0 kPa. If the measured object is not a human body, the first pressure may be further increased. However, if the measured object is a human body, the first pressure is preferably not excessively increased to prevent pain.
According to the present invention, correlation with body fat is improved and quantitative determination accuracy for body fat is increased by employing the wavelength region of 1.1 to 2.0 xcexcm having a large absorption coefficient of fat, making measurements while varying the pressure for compressing the measured region or the peripheral portion thereof in two stages and obtaining the difference between the absorbance values under the two compressed states.
When measuring body fat of a human body with the inventive measuring apparatus, quantitative data useful for health care can be provided.
When applying the measuring apparatus and the measuring method according to the present invention to a physical mass other than a human body, body fat of an animal or fish for edible meat can be measured in a live. state for controlling the quality of the meat The body fat of a physical mass other than a human body must be measured also in a carcass state before and after dissociation. Therefore, the measuring apparatus and the measuring method according to the present invention can provide quantitative data useful for quality control of a physical mass other than a human body.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawing.